This invention relates generally to emission spectroscopy and more particularly to an apparatus for emission spectrochemical analysis which utilizes spark discharges or pulses of a laser beam.
There is known a method of emission spectrochemical analysis in which spark discharges or pulses of a laser beam are applied to a sample to be analyzed to cause the sample to emit light, which is analyzed spectroscopically. The method has the following problem: In emission spectrochemical analysis using spark discharge, it is customary to pretreat the surface of a sample to be analyzed by applying spark discharges to the sample surface before analysis is conducted so as to reduce the adverse influence of small scars and/or pinholes on or in the sample surface and/or foreign matter, thereby improving the precision of analysis. For example, for analysis of a sample for 5 seconds the sample must be pretreated with high-energy spark discharges for more than 10 seconds.
The spark discharges for pretreatment of a sample may be referred to as the "preparatory discharges", while the spark discharges for analysis may be referred to as the "analytic discharges".
The reason why the preparatory discharge and the analytic discharge are conducted separately is as follows: Although high-energy discharge has a great capacity for vaporizing a sample, the resulting background light is strong as compared with the spectral line intensity of the component elements of the sample, with resulting decrease in the sensitivity of analysis. Therefore, low-energy discharge is suitable for analysis itself. Thus, after high-energy preparatory discharges have been conducted on a sample for 5 to 10 seconds, several thousand low-energy analytic discharges are conducted to analyze the light from the sample.
If the energy for analytic discharge is too low, however, the amount of the sample components vaporized decreases and the intensity of the light of the spectral emission lines produced becomes weak, with resulting reduction of the sensitivity and precision of analysis. Therefore, a sufficient amount of the sample must be vaporized by analytic discharges, so that there is a limit to which the energy level of the analytic discharges can be lowered, with resulting difficulty in reducing the background light.
As mentioned above, the time required for preparatory discharges is longer than the time required for analytic discharges. The reason why this is so is that the position in the surface of a sample which is struck by each of the spark discharges produced in one operation of analysis is uncertain, so that the whole area of the sample surface must be treated beforehand by preparatory discharges. To improve the precision of analysis a longer period of time is required for preparatory discharge.
Since a sufficient amount of the sample must be vaporized in analytic discharge, the energy for analytic discharge cannot be reduced to a very low level, with resulting difficulty in reducing the background light and obtaining a high sensitivity.
The present inventors have once proposed a method of spectro-chemical analysis of a sample containing elements to be analyzed, in which high-energy pulses are cyclically applied onto a small area of a sample to vaporize the components of the sample from the small area thereof, and low-energy spark discharges are generated by a spark generator including an electrode facing the sample so as to be applied to the small area of the sample a predetermined period of time after the application of each high-energy pulse and during the time in which the vaporized components of the sample caused by the application of high energy remains between the sample and the electrode, and the light emitted by the sample vapor while the low-energy spark discharges are being conducted is spectroscopically measured.
The characteristic of the above-mentioned prior invention is that each and every one of the emissions of light from the sample being analyzed comprises a step of vaporizing the sample and that of analyzing the vaporized elements of the sample. With the method of the prior invention, it is possible to analyze a sample at a cleaned spot on the surface thereof by low-energy spark discharge without pretreatment by conventional preparatory discharge, and to obtain a high sensitivity due to the lowered background level. The circuit arrangement, however, is complicated. In the prior art arrangement the output from the measuring circuit is amplified and sampled by a switching circuit operated synchronously with each emission of light from the sample, and one measuring channel must be provided for each one of the spectral lines of the elements in the sample, and one switching circuit is required for each measuring channel, with resulting complication of the whole circuit arrangement.
Accordingly, the primary object of the invention is to simplify the circuit arrangement used in an apparatus for emission spectro-chemical analysis which uses a time resolution method of measuring the spectral intensity of light emissions from a sample caused by spark discharge pulses each comprising a high-energy and a low-energy portion.